Nickel-chromium alloys and casting thereof

ABSTRACT

A nickel-chromium-cobalt alloy containing correlated percentages of niobium, tantalum, titanium, aluminum and also chromium affords high stress-rupture lives in elevated temperatures.

United States Patent Shaw 5] Dec. 9, 1975 [5 NlCKEL-CHROMIUM ALLOYS AND [56] References Cited CASTING THEREOF UNITED STATES PATENTS [75] Inventor: Stuart Walter Ker Shaw, Sutton 3,589.893 6/1971 Lund et all 75/l7l Coldfield, England 73 Assignee: The International Nickel Co., Inc., "Mary 5- Dean New York NY. Attorney, Agent, or FirmRaymond J. Kenny; Ewan C. MacQueen [22] F1led: Apr. 12, 1974 [21} Appl. No.: 460,460 [57] ABSTRACT [30] Foreign Application Priority Data Apr [3 973 United Kingdom H 7951/73 A nickel-chromium-cobalt alloy containing correlated percentages of niobium, tantalum, titanium, aluminum [52] us Cl. H 75/171; 75/134 F; 148/3; and also chromium affords high stressqupture lives in 148/13; 148/32; 148/325; 148/l62 e'evated ternPmmms- [51] Int. Cl. C22C 19/05 [58} Field of Search 75/171, 170, I34 P;

7 Claims, No Drawings NICKEL-CHROMIUM ALLOYS AND CASTING THEREOF The subject invention is addressed to nickelchromium alloys and is directly concerned with articles and parts cast therefrom and which are intended for use under high orders of stress at elevated temperatures, particularly under corrosive conditions.

in US. Pat. application Ser. No. 254,728, 1 described various nickel-chromium alloyscontaining, by weight, from 27 to 31% chromium, from 10 to 25% cobalt, from to 1.9% niobium, both titanium and aluminum in a total amount from 3.5 to 5.5%, but with the provisos that the ratio of titanium to aluminum be from 1:1

to 4:1 and that the sum of 5(%Nb) 6(%Ti at A1) 16 91) Cr) be from 49 to 54. The alloys also encompassed from 0.02 to 0.2% carbon, up to 0.6% zirconium, up to 1.2% hafnium, with the value of Zr 0.5 Hf) being not more than 0.6%, up to 0.02% boron, and up to 0.2% in total of yttrium and/or lanthanum, the balance being essentially nickel.

The above alloys have remarkably good stress-rupture lives in the casts form but should the relationship 5 Nb) 6(%Ti A1) 36 (%Cr) have exceeded 54 the stress-rupture life of the alloys could be expected to fall off. A noted drawback was the apparent inherent tendency to form sigma, an embrittling phase, upon high temperature exposure for but moderate periods of time. Therefore, the problem, at least in part, involved how to achieve yet higher stress-rupture strengths but without incurring other detrimental setbacks.

In any case, it has now been found that enhanced stress-rupture lives can be attained with cast ailoys of generally similar composition as above described notwithstanding that the value for relationship above given well exceeds 54, provided, however, that (i) the alloy also contain both tungsten and tantalum, (ii) niobium be necessarily present, and (iii) the contents of tungsten, tantalum, titanium, aluminum, niobium and chromium are correlated as required herein.

Generally speaking, the present invention contemplates articles and parts cast from alloys containing, by weight, from 26 to 35% chromium, about 10 to 25% 2 cobalt, about 0.1 to 0.6% niobium, about 0.3 to 1.5% tungsten, about 1 to 3% tantalum, about 2.5 to 5% titanium, about 1 to 2.5% aluminum, the titanium and aluminum being found in a total amount of about 4.3 to 5.75% and with the provisos that the ratio of titanium to aluminum be from 1.411 to 4:1 by weight and that be from 54.5 to 61.3, about 0.05 to 0.15% carbon, about 0.02 to 0.5% zirconium, about 0.002 to 0.05% boron, from 0 to 2% hafnium, and from 0 to 0.2% in total of yttrium and/or lanthanum, the balance, apart from impurities, being essentially nickel, the nickel preferably being present in an amount of at least 35%.

in seeking an optimum combination of properties, it is advantageous that the alloys from which articles and parts are cast contain from 27 to 33% chromium, from 10 to 20% cobalt, from 0.1 to 0.6% niobium, from 0.5 to 1.0% tungsten, from 1.5 to 2.8% tantalum, from 2.5 to 4.0% titanium, from 1.3 to 2.2% aluminum, both titanium and aluminum in a total amount of 4.3 to 5.75%, from 0.06 to 0.12% carbon, from 0.03 to 0.2% zirconium, from 0.003 to 0.02% boron, and the balance nickel.

A particularly useful alloy for cast articles and parts, according to the invention contains about 28.6% chromium, about 14.7% cobalt, about 0.6% tungsten, about 0.3% niobium, about 2.66% tantalum, about 3.59% titanium, about 1.96% aluminum, about 0.1% carbon, about 0.1 1% zirconium, about 0.015% boron, the balance being nickel.

By way of example, articles and parts according to the invention were cast from Alloys 1 to 8 and compared in stress-rupture and impact strength tests with articles and parts outside the scope of the invention cast from Alloys A to L with the results being set forth in Table 1. All the alloys were vacuum melted and test pieces were machined from cast blanks of the particular alloys which had been treated by heating for 4 hours at 1150C., air-cooled, heated at 850C. for 16 hours and air cooled. Stress-rupture values are given in Table 1 obtained under a stress of 139 N/mm (Newtons per square millimeter) at 870C. together with impact strength values obtained by a Charpy test after 1000 hours at 850C.

TABLE 1 Analyzed Composition wt. bal. Ni Alloy Nb Ti/Al No Cr Co W Nb Ta l Ta Ti Al Ti+Al 1.8:1 Zr B A 0.10 28.6 14.8 0.55 0.32 2.52 1.58 3.84 1.97 5.81 1.95 0.11 0.015 B 0.09 28.2 14.6 0.73 0.35 2.47 1.59 3.90 1.89 5.79 2.06 0.04 0.011 1 0.09 28.7 14.7 0.72 0.32 2.54 1.59 3.68 2.01 5.69 1.83 0.11 0.013 2 0.10 28.8 14.9 0.60 0.32 2.55 1.60 3.48 1.97 5.45 1.77 0.11 0.015 3 0.09 28.2 14.6 0.58 0.34 2.46 1.57 3.47 1.90 5.37 1.83 0.04 0.012 4 0.08 28.2 15.5 0.69 0.22 2.58 1.51 3.55 1.70 5.25 2.09 0.11 0.011 5 0.08 28.9 14.7 0.70 0.32 2.55 1.60 3.42 1.80 5.22 1.90 0.10 0.014 6 0.10 29.0 14.5 0.88 0.48 1.70 1.33 3.30 1.75 5.05 1.88 0.11 0.011 7 0.09 30.4 14.6 0.94 0.38 2.35 1.66 2.80 1.70 4.50 1.97 0.11 0.011 8 0.09 30.4 14.6 0.94 0.38 2.35 1.66 2.70 1.70 4.40 1.59 0.11 0.011 C 0.08 30.4 14.6 0.75 0.37 2.40 1.57 2.70 1.50 4.20 1.80 0.11 0.010 D 0.09 29.2 14.8 0.69 0.31 2.56 1.59 2.60 2.02 4.62 1.29 0.10 0.014 E 0.09 29.2 14.7 0.73 0.30 2.56 1.58 2.36 1.97 4.33 1.20 0.11 0.014 F 0.08 28.4 14.7 0.79 0.05 2.56 1.28 3.44 1.88 5.32 1.83 0.10 0.013 O 0.11 29.6 15.0 0 0.70 2.0 1.70 3.00 1.52 4.52 1.97 0.12 0009 H 0.05 28.5 20.4 1.50 1.50 3.15 1.80 4.95 1.75 0.065 0.004 1 0.06 28.3 20.3 1.60 1.60 2.65 1.67 4.32 1.59 0.065 0.004 .1 0.06 28.3 20.3 1.60 1.60 2.30 1.44 3.74 1.60 0.065 0.004 K 0.06 28.1 19.6 0.52 0.52 3.30 1.95 5.25 1.69 0.095 0.005 L 0.06 28.3 20.1 1.15 1.15 3.20 1.77 4.97 1.81 0.070 0.004

5 (Nb 1% Ta) Impact Strength Alloy Life at 6 (Ti A1) after TABLE l-continued Analyzed Composition wt. bal. Ni

Alloy Nb Ti/Al No. C Cr Co W Nb Ta 6 Ta Ti Al TH-Al 1.8:] Zr B No. 139 N/mml870 C. 2/3 (Cr) l000h/850C. J

6 1731 56.3 ND. 7 1655 55.6 ND. 8 1591 55.0 ND. C 1516 53.4 N.D. D 1366 55.1 18

H 740 562 ND.

J 851 49.3 N.D

K 1279 52.8 N.D

ND. Not Determined J Joule (Charpy) N/mm': Newtons per square millimeter From the data of Table 1 it can be seen that articles and parts according to the invention cast from alloys 1 to 8 containing, by weight, from 28.2 to 30.4% chromium, from 14.6 to 15.5% cobalt, from 0.22 to 0.48% niobium, from 0.6 to 0.94% tungsten, from 1.7 to 2.58% tantalum, from 2.7 to 3.68% titanium, from 1.7 to 2.01% aluminum, 4.4 to 5.69% titanium plus aluminum, ratio of titanium to aluminum from 1.59:1 to

being in the range of from 55 to 61.2, from 0.08 to 0.10% carbon, from 0.04 to 0.11% zirconium, from 0.01 l to 0.015% boron, the balance, apart from impurities, being nickel, had stress-rupture lives at 139 ltl/mm and 870C. in excess of 1550 hours and typically of the order of 1591 to 1895 hours. Such castings according to the invention also had impact strengths after 1000 hours at 850C. in excess of Joules and typically of the order of 18 to 20 J.

Articles outside the invention cast from Alloys A to L had stress-rupture lives at 139 N/mm and 870C. of less than 1520 hours and typically of the order of 740 to 1516 hours. Such articles cast from Alloys A to L had impact strengths after 1000 hours at 850C. up to J and typically of the order of 7 to 25 J. Thus articles of the invention have a high stress-rupture life coupled with a consistently good impact strength in comparison with similar articles outside the invention which have poorer stress-rupture lives coupled with inconsistent impact strength.

In high temperature nickel base alloys containing niobium, titanium, aluminum and chromium it is usually necessary to set the maximum content of these constituents at a specific figure because higher contents cause sigma phase formation in the alloy after moderate times at service temperatures leading to embrittlement and alloy failure. As indicated previously, in the case of the aforementioned alloys of Patent Application No. 254,728, this consideration necessitated that maximum value for the relationship 5 (%Nb) 6 (%Ti %Al) (%Cr) not exceed 54. In marked departure therefrom, in accordance with the instant invention when tungsten and tantalum are present, stronger alloys can be produced though the value 54 be exceeded for the given relationship (including tantalum with niobium on an equiatomic basis, i.e., 5 [%Nb (%Ta)] without formation of embrittling sigma phase. What would be the complete theoretical metallurgical explanation of this surprising behavior is not presently understood.

As can be seen by comparing from Table 1 Alloy E, which contained 2.56% tantalum, 0.30% niobium that is a [%Nb /(%Ta)] value of 1.58%, and 0.73% tungsten, and Alloy l which contained 1.60% niobium and no tantalum or tungsten, the mere inclusion of tantalum and tungsten alone does not strengthen the alloy as Alloy E had a stress-rupture life of 1154 hours and Alloy I a stress-rupture life of 1282 hours. For improvement of the strength and hence the stress-rupture life of the alloy it is also necessary to correlate the total niobium, tantalum, titanium, aluminum and chromium content. Alloy E only had a value of 53.4 and Alloy l a value of 52.8 as given by the relationship:

5[%Nb A (%Ta)] 6 (%Ti %A1)+ "A (%Cr) whereas it can be seen from Table 1 that castings of the invention made from Alloys 1 to 8 had considerably improved stress-rupture lives when the relationship value was in the range 54.5 to 61.3.

In futher attempting to compare alloys within vs. alloys without the invention, it can be seen that Alloys C and E with relationship values of 53.4 had stress-rupture lives of 1516 and l 154 hours, respectively, whilst Alloys A and B with the relationship values of 61.8 and 61.4, had stress-rupture lives of 1184 and 1192 hours, respectively. Thus, relationship values below and above the range of 54.5 to 61.3 can reduce stress-rupture life considerably. in the absence of tungsten and tantalum, even alloys with a relationship value in the range 54.5 to 61.3 had poorer stress-rupture lives as can be seen from Alloy L (relationship value 54.5 and stress-rupture life 843 hours) and Alloy H (relationship value 56.2 and stressrupture life 740 hours). Alloys L and A had impact strengths of 8 J and 7 J, respectively, indicating embrittlement due to sigma phase formation.

The best stress-rupture lives are shown according to the invention by Alloys 2 to 6 which had stress-rupture lives in excess of 1720 hours for a relationship value range of 56 to 60. Thus, most preferably, articles and parts according to the invention are cast from alloys containing, about 28 to 29% chromium, about 14.5 to 15.5% cobalt, about 0.22 to 0.48% niobium, about 0.58 to 0.88% tungsten, about 1.7 to about 2.58% tantalum, about 3.3 to 3.48% titanium, about 1.75 to 2% aluminum, about 5 to 5.5% titanium plus aluminum, with the ratio of titanium to aluminum from 1.77:1 to 2.09:1,

and with the sum of 51%Nb a (%Ta)] 6 (%Ti %Al) 55 (%Cr) being in the range of from 56 to 60, about 0.08 to 0.10% carbon, about 0.04 to 0.11% zirconium, about 0.01 1 to 0.015% boron, the balance, apart from impurities, being essentially nickel.

Total titanium plus aluminum contents in excess of 5.75% unsatisfactorily reduce the stress-rupture life as can be seen by comparing Alloy A (life 1184 hours at Ti A1 of 5.81%) Alloy B (life 1192 hours at Ti A1 of 5.79%) and Alloy 1 (life 1680 hours at Ti A1 of 5.69%). Total titanium plus aluminum contents below 4.3% reduce the stress-rupture life as can be seen by comparing from Table 1 Alloy 8 (life 1591 hours at Ti A1 of 4.40%) and Alloy C (life 1516 hours at Ti -1- A1 of 4.20%). It is of benefit that the Ti Al content be in the range of about 4.40 to 5.69% and more advantageously, in the range of 5.0 to 5.5%.

A ratio of titanium to aluminum of less than 1.4:1 reduces the stress-rupture life to an undesirable extent even when the alloy contains an otherwise acceptable total amount of titanium and aluminum. This can be seen from Table l by comparing Alloy D (life of 1366 hours at Ti/Al of 1.29:1) and Alloy E (life of 1154 hours at Ti/Al of 1.20:1) with Alloy 8 (life of 1591 hours at Ti/Al of 1.59:1 Indeed Alloy E which contains 2.36% titanium also shows that titanium contents of less than 2.5% undesirably reduce the stress-rupture life.

A niobium content of less than 0.1% or the absence of niobium, reduces the stress-rupture life as can be seen from the results of Alloy F in Table 1. Alloy F with less than 0.05% niobium but with an advantageous Ti Al content of 5.32 and relationship value of 57.2 and Alloy G with a stress-ruptu re life of 1053 hours at a niobium content of 0.70%, an acceptable Ti A1 content of 4.52% and an acceptable relationship value of 55.4, show that niobium contents in excess of 0.60% unsatisfactorily reduce the stress-rupture life. Preferably articles and parts according to the invention are cast from alloys containing from 0.22 to 0.48% niobium.

Reducing the zirconium content is thought to reduce the stress-rupture life as may be seen by comparing from Alloy 3 (life of 1720 hours at 0.04% zirconium) with Alloy 5 (life of 1895 hours at 0.1 1% zirconium). Preferably, the zirconium content should be in the range of from 0.03 to 0.2%, and more preferably, in the range 0.04 to 0.11%.

Articles and parts according to the invention may be blades and other components of gas turbine engines, and are also suitable for other applications where good stress-rupture life at high temperatures in corrosive environments is required.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations can be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and appended claims.

1 claim:

1. A cast alloy consisting essentially of, by weight, from 26 to 35% chromium, from 10 to 25% cobalt, from 0.1 to 0.6% niobium, from 0.3 to 1.5% tungsten, from 1 to 3% tantalum, from 2.5 to 5% titanium, from 1 to 2.5% aluminum, both titanium and aluminum in a total amount from 4.3 to 5.75% with the provisos that the ratio of titanium to aluminum is from 1.4:1 to 4:1 by weight and that the sum 5 [%Nb+ memo 6 (%Ti %Al) as (%Cr) is from 54.5 to 61.3, from 0.05 to 0.15% carbon, from 0.02 to 0.5% zirconium, from 0.002 to 0.05% boron, from 0 to 2% hafnium, and from 0 to 0.2% in total of yttrium and/or lanthanum, the balance, apart from impurities, being nickel.

2. A cast alloy according to claim 1 containing 27 to 33% chromium, 10 to 20% cobalt, 0.5 to 1.0% tungsten, 1.5 to 2.8% tantalum, 2.5 to 4.0% titanium, 1.3 to 2.2% aluminum, 0.06 to 0.12% carbon, 0.03 to 0.2% zirconium, 0.003 to 0.02% boron, the nickel being at least 35%.

3. A cast alloy according to claim 2 containing 28.2 to 30.4% chromium, 14.6 to 15.5% cobalt, 0.22 to 0.48% niobium, 0.6 to 0.94% tungsten, 1.7 to 2.58% tantalum, 2.7 to 3.68% titanium, 1.7 to 2.01% aluminum, 4.4 to 5.69% titanium plus aluminum, ratio of titanium to aluminum from 1.59:1 to 2.09:1 sum of 5 [%Nb+ A (%Tall 6 (%Ti %A1) as 1%Cr) being in the range of from 55 to 61.2, 0.08 to 0.10% carbon, 0.04 to 0.11% zirconium and 0.011 to 0.015% boron.

4. A cast alloy according to claim 2 containing 28 to 29% chromium, 14.5 to 15.5% cobalt, 0.22 to 0.48% niobium, 0.58 to 0.88% tungsten, 1.70 to 2.58% tantalum, 3.30 to 3.48% titanium, 1.75 to 2% aluminum, 5.0 to 5.5% titanium plus aluminum, ratio titanium to am minum from 1.77:1 to 2.09:1, sum of 51%Nb+ I: (m-.111 6 (%Ti +%A1) ts 1%0] being in the range of from 56 to 60, 0.08 to 0.10% carbon, 0.04 to 0.11% zirconium and 0.011 to 0.015% b0- ron.

5. A cast alloy according to claim 2 containing 28.6% chromium, 14.7% cobalt, 0.6% tungsten, 0.3% niobium, 2.66% tantalum, 3.59% titanium, 1.96% aluminum, 0.1% carbon, 0.1 1% zirconium and 0.015% boron.

6. A cast component of the composition set forth in claim 2, which has been heat treated at 1 C, for 4 hours and air cooled followed by heat treatment at 850C for 16 hours and air cooled.

7. A component cast from the composition set forth in claim 2.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENT NO. 1 3,925,072

D TED i December 9, 1975 INVENTORIS) i STUART WALTER KER SHAW It rs certified that error appears in the above-Identified patent and that sard Letters Patent are hereby corrected as shown below Column 1, line 25, for "casts read -cast--.

The column headings directly beneath the bottom line under "TABLE I" 5(Nb 1/2 Ta) Impact Strength Alloy Life at +6 (Ti Al) after should be removed from this location and inserted on the following page directly under the heading "TABLE I-continued and in place of the following headings which should be deleted:

Analyzed Composition wt.% bal. Ni

Alloy Nb+ Ti/Al No. C Cr Co W Nb Ta l/2Ta Ti Al Ti+Al 1.8:1 Zr B Signed and Scaled this fourth Day of May 1976 [sen] Arrest:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mmnissium'r of Put; an and Tradenmrks 

1. A CAST ALLOY CONSISTING ESSENTIALLY OF, BY WEIGHT, FROM 26 TO 35% CHROMIUM, FROM 10 TO 25% COBALT, FROM 0.1 TO 0.6% NIOBIUM, FROM 0.3 TO 1.5% TUNGSTEN, FROM 1 TO 3% TANTALUM, FROM 2.5 TO 5% TITANIUM, FROM 1 TO 2.5% ALUMINUM, BOTH TITNIUM AND ALIMINUM IN A TOTAL AMOUNT FROM 4.3 TO 5.75% WITH THE PROVISOS THAT THE RATIO OF TITANIUM TO ALUMINUM IS FROM 1.4: TO 4.1 BY WEIGHT AND THAT THE SUM
 2. A cast alloy according to claim 1 containing 27 to 33% chromium, 10 to 20% cobalt, 0.5 to 1.0% tungsten, 1.5 to 2.8% tantalum, 2.5 to 4.0% titanium, 1.3 to 2.2% aluminum, 0.06 to 0.12% carbon, 0.03 to 0.2% zirconium, 0.003 to 0.02% boron, the nickel being at least 35%.
 3. A cast alloy according to claim 2 containing 28.2 to 30.4% chromium, 14.6 to 15.5% cobalt, 0.22 to 0.48% niobium, 0.6 to 0.94% tungsten, 1.7 to 2.58% tantalum, 2.7 to 3.68% titanium, 1.7 to 2.01% aluminum, 4.4 to 5.69% titanium plus aluminum, ratio of titanium to aluminum from 1.59:1 to 2.09:1 sum of 5 (%Nb + 1/2 (%Ta)) + 6 (%Ti + %Al) + 2/3 (%Cr) being in the range of from 55 to 61.2, 0.08 to 0.10% carbon, 0.04 to 0.11% zirconium and 0.011 to 0.015% boron.
 4. A cast alloy according to claim 2 containing 28 to 29% chromium, 14.5 to 15.5% cobalt, 0.22 to 0.48% niobium, 0.58 to 0.88% tungsten, 1.70 to 2.58% tantalum, 3.30 to 3.48% titanium, 1.75 to 2% aluminum, 5.0 to 5.5% titanium plus aluminum, ratio titanium to aluminum from 1.77:1 to 2.09:1, sum of 5 (%Nb + 1/2 (%Ta)) + 6 (%Ti + %Al) + 2/3 (%Cr) being in the range of from 56 to 60, 0.08 to 0.10% carbon, 0.04 to 0.11% zirconium and 0.011 to 0.015% boron.
 5. A cast alloy according to claim 2 containing 28.6% chromium, 14.7% cobalt, 0.6% tungsten, 0.3% niobium, 2.66% tantalum, 3.59% titanium, 1.96% aluminum, 0.1% carbon, 0.11% zirconium and 0.015% boron.
 6. A cast component of the composition set forth in claim 2, which has been heat treated at 1150*C, for 4 hours and air cooled followed by heat treatment at 850*C for 16 hours and air cooled.
 7. A component cast from the composition set forth in claim
 2. 